1. Field of the Invention
The present invention relates generally to an active matrix type liquid crystal display panel as is indicated. In particular, the present invention relates to an active matrix type liquid crystal display panel having a construction capable of preventing breakdown of the switching elements or deterioration of the characteristics thereof due to static electricity or the like which can arise in the production process. The invention also relates to a method for producing such an active matrix type liquid crystal display panel.
2. Description of the Related Art
FIG. 3 shows the equivalent circuit of a conventional active matrix type liquid crystal display panel. As is known, such a conventional liquid crystal display panel generally includes an active matrix substrate serving as a first insulating substrate, a counter substrate serving as a second insulating substrate, and a liquid crystal layer which serves as a display medium. The active matrix substrate and the counter substrate are positioned so as to face each other with the liquid crystal layer interposed therebetween. As shown in FIG. 3, the liquid crystal display panel also includes counter electrodes 39 which are formed on almost the entire surface of the counter substrate on the side facing the display medium. On the surface of the active matrix substrate on the side facing the display medium, gate bus lines 31 serving as scanning lines and source bus lines 32 serving as signal lines are so located that the gate bus lines 31 intersect the source bus lines 32. In each of the areas surrounded by the gate bus lines 31 and the source bus lines 32, a thin film transistor (hereinafter referred to as a "TFT") 33 functioning as a switching element and a pixel electrode 38 are provided.
The TFT 33 is connected to the gate bus line 31, source bus line 32 and pixel electrode 38 as shown. The TFT 33 receives a gate signal transmitted through the gate bus line 31, and is turned on or off in accordance with the received gate signal. When the TFT 33 is turned on, it receives a source signal transmitted through the source bus line 32, and transfers the received source signal to the pixel electrode 38. The pixel electrodes 38 formed on the active matrix substrate are positioned so as to face respectively the above-mentioned counter electrodes 39 formed on the counter substrate, with the liquid crystal layer interposed therebetween. Each pixel electrode 38, the counter electrode 39 corresponding thereto, and the portion of the liquid crystal layer interposed therebetween form a liquid crystal cell 34 which functions as a capacitor.
The liquid crystal display panel further includes a short-circuit line 36 and non-linear elements 37 formed on the active matrix substrate. The short-circuit line 36 is connected to an end of each gate bus line 31 and also to an end of each source bus line 32 by way of a corresponding non-linear element 37. The non-linear element 37 functions as an element having low resistance when static electricity arises, so that electric charges of the static electricity are diffused through the short-circuit line 36. Due to such diffusion, electric potentials of the gate bus line 31 and the source bus line 32 become equal to each other. As a result, breakdown of the TFTs 33 or deterioration of the characteristics thereof due to the static electricity arising in the production process of the liquid crystal display panel can be prevented. The non-linear element 37 used in this conventional liquid crystal display panel is composed of, for example, a TFT.
The reason for providing the non-linear elements 37 is as follows. In cases where the short-circuit line 36 is directly connected to the gate bus lines 31 and source bus lines 32 without using the non-linear elements 37, it is necessary to cut or otherwise remove the peripheral portions of the liquid crystal display panel in order to remove the short-circuit line 36 therefrom after the production of the liquid crystal display panel has been completed. The removal of the short-circuit line 36 after production of the liquid crystal display panel is disadvantageous, however, in that the liquid crystal display panel without the short-circuit line 36 is exposed to static electricity in subsequent processes such as inspection of the liquid crystal display panel, assembly of an apparatus using the liquid crystal display panel, and the like. Since the short-circuit line 36 functions to protect the TFTs 33 (switching elements) from static electricity as described above, the switching elements in the liquid crystal display panel without such short-circuit line are easily broken down or deteriorated by static electricity in the above-mentioned inspection and assembly processes.
To solve this problem, the conventional liquid crystal display panel shown in FIG. 3 uses the non-linear elements 37 which eliminate the necessity of removing the short-circuit line 36 from the liquid crystal display panel after the production thereof. Even when the liquid crystal display panel is exposed to static electricity in the above-mentioned inspection and assembly processes, the short-circuit line 36 which remains therein prevents breakdown or deterioration of the TFTs 33 due to such static electricity. Therefore, the conventional liquid crystal display panel is advantageous in that breakdown of the switching elements or deterioration of the characteristics thereof due to static electricity can be prevented during both the production process and the subsequent inspection and assembly processes.
With such a conventional liquid crystal display panel, however, since the non-linear elements 37 are composed of TFTs or the like as described above, additional production steps are required for the fabrication of the non-linear elements 37. For example, an etching process is required to provide through holes for the TFTs. Accordingly, the entire production process of the liquid crystal display panel becomes complicated. Furthermore, because each non-linear element consists of a TFT there is a greater possibility that a charge leak will occur in the non-linear element 37 to cause a defect in the liquid crystal display panel.